Art of casting metals

ABSTRACT

An inert gas welding torch is used to create plasma by directing one or more discrete high velocity jet gas streams into a welding arc between the electrode and the workpiece. The plasma stream is controllable with regard to energy content or location by varying the amount or direction of the inert gas flow. The plasma stream is insensitive to variations of arc length, and permits abnormally high current densities in the electrode. When used with consumable electrodes, the invention is useful for casting as well as for deep welding heavy plate materials in a single pass.

o 1 Elite 4.11 States atent H 1 [111 3,865,473

ohrherg Feb. 11, 1975 [54] THE ART OF CASTlNG METALS 5,825,080 3/1938Merrick 164/252 X 52,001 I962 Brennan 164/251 1 lhvehlofl Rdemk TorranceCahf- 3,506,057 4/1970 Pennock 61611 164/19 [73] Assigheesl 2 h gh g t dFOREIGN PATENTS OR AIPPLICATIONS orpora ion; 1r r0 uc s an ChemicalsInc. both of Allentown. 816,565 5/1937 France [64/289 Pa. part interestto each Pnmary E.\'amu1er-R. Spencer Annear Flledi p 1 1970 Allorney,Agent. or Firm.lames C. Simmons; Barry 21 Appl. No.: 43,643 MyermanBelated US. Application Data [57] ABSTRACT by 365 b l6, lgmabandonedd1rect1ng one or more discrete hlgh velocity jet gas streams into awelding are between the electrode and 52 us. c1 164/46, 164/52, 164/114,the WerkPieee- The Plesma Stream is Controllable with 164/289 regard toenergy content or location by varying the 511 um. c1 322d 27/02 amountor direction Of the inert gas The Plasma [58] Field of Search 164/19, 4652, 66, 114, stream is insensitive to variations of arc length, and

164/251 252, 259, 219/121 p 122 permits abnormally high currentdensities in the electrode. When used with consumabie electrodes, thein- [56] References Cited vention is useful for casting as well as fordeep Welding UNITED STATES PATENTS heavy plate materials in a singlepass. 1,638,336 8/1927 Himes 219/122 x 3 Claims, 28 Drawing Figures O fl5 2|;

PATENTEUFEBI H915 3.865.173

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POWER SOURCE 2 INVENTOR. FIG. 6 RODERICK G. ROHRBERG ATTORNEY Pmzmimw3.865.173

' I saw BM 6 M ZI fl/O 533555 5 ILMNHIEF s f/IO POWER SOURCE POWERSOURCE INVENTOR. RODERICK G. ROHRBERG mum ATTORNEY PATENTED 3,865,173

SHEET 50F 6 ISOW INVENTOR.

RODERICK G. ROHRBERG QwARQX ATTORNEY PAIENTEDFEBI H915 3.865.173

SHEEI 6 OF 6 I N VEN TOR. RODERICK G. ROHRBERG ATTORNEY THE ART OFCASTING METALS This application is a division of copending applicationSer. No. 830,565, filed May 8, 1969, now U.S. Pat. No. 3,604,889, whichis a continuation-in-part of copending Application Ser. No. 693,365filed Dec. 16, 1967 now abandoned.

BACKGROUND OF THE INVENTION This invention includes and contemplatesprogressive fusion welding of metallic components along a predeterminedpath to form a permanent joint between the same. The invention isparticularly pertinent to such joints having substantial depth, such asone quarter inch to one full inch of workpiece thickness, for example,and to joints normally requiring two or more successive passes of theelectrode over all or some portion of the weld area to complete thejoint using prior art methods.

The invention in this case combines certain features associated withconventional tungsten inert gas (TIG) as well as MIG (consumableelectrode) welding and also with conventional plasma torch technologyknown to the prior art. Thus, TIG and MIG welding as currently practicedinvolve provision of a welding power source connected with an alectrodewhich is positioned close enough to a workpiece to produce a flow ofcurrent across the space or gap between the electrode and workpiece whenthe two are in circuit with the power source. A gas shroud surrounds theelectrode and isolates the are from surrounding atmosphere to minimizeoxidation of molten metal in the weld puddle. The shape of the arc isessentially uncontrollable, and the inherent tendency of the currentflow to pass through the electrode to the nearest workpiece portionnecessitates care to prevent arcing at any place other than theelectrode tip during deep welding within workpiece components havingsubstantial thickness. Such uncontrolled arcing, as experienced in priorart methods, produces localized heating on one workpiece componentwithout significant heating of the other such component as required tojoin the two together.

Plasma torches known to the prior art generally involve an elongatechamber such as a cylindrical body containing either a disc-type or apenciltype cathode axially situated and spaced apart from a circularanode surrounding an exit opening. Inert gas supplied to the chamber isionized by passage through the electrical are established between thecathode and anode, exiting as a plasma stream through the stated exitopening. Electrode erosion, especially of the anode, is a commonplaceproblem in plasma torches widely known and used in industry. Sucherosion is more rapid when the electrode is not effectively cooled, andsuch cooling is particularly difficult in plasma torches due to theextremely high temperature of the wholly contained are within thechamber.

With further regard to background knowledge in the prior art, it haslong been known that either an electric are or a plasma stream may bealtered in shape or location by directing external streams of shieldinggas closely proximate such are or stream. Typical of the issued US.patents relating to stabilization of an electric are by surrounding thesame with gas streams are the following: 1,638,336 issued Aug. 9, 1 927;2,554,236 issued May 22, 1951: 2,798,145 issued July 2, 1957; 3,238,349issued Mar. 1, 1966; and 3,251,977 issued may 17, 1966. Issued U.S.patents involving or suggesting external gas shields to stabilize orotherwise shape a plasma stream include the following: 2,806,124 issuedSept. 10, 1957; 2,868,950 issued Jan. 13, 1959; 3,076,085 issued Jan.29, 1963; 3,272,962 issued Sept. 13, 1966; and 3,349,215 issued Oct. 24,1967.

SUMMARY OF THE INVENTION The inventive concept in this case isparticularly suited for converting standard inert gas welding torchesinto plasma torches. Although the plasma thus produced may be used fordiverse purposes and in different ways, the inventive concept disclosedherein will be described in connection with fusion welding. Existingelectrode mounts of standard well-known type used for TIG or MIG fusionweldidng torches may be easily modified to incorporate the teachingscontained herein. Essentially, the changes required to convert suchtorches for plasma generation consist of providing one or mo re inertgas jet streams so oriented as to penetrate into an electrical arebeyond or proximate the electrode tip, as distinguished from gas flow ina direction parallel to the dominant direction of current flow in suchare, and drastically increasing both the current and gas flow rate abovethose associated with welding or with mere arc shielding and stabilizingas practiced in the prior art. lllustratively, a plurality of highvelocity inert gas jet streams may be arranged symmetrically about theelectrode and adapted to converge together at a focal point located onthe longitudinal axis of the electrode.

The maximum current which can safely be applied to the electrode whenused for conventional TIG or MIG welding may be roughly doubled when thesame electrode is converted for use as a plasma generator. Moreover, nosignificant electrode erosion results from use of typical TIG weldingelectrodes, due to the cooling effect of the high inert gas llow ratedirected into the are. This aspect of the process disclosed herein isparticularly important, since cooling problems are totally eliminatedwhen the plasma-creating electrical arc is totally exposed and notconfined within a chamber or other container as is the case withconventional plasma torches known to the prior art. Moreover, consumableelectrode welding torches, when modified according to the novelteachings in this case, possess a particular versatility forapplications requiring placement of molten metal in closely confinedlocations such as deeply within a welding gap between two confrontingworkpiece elements, or with corners or even within the center of a moldas discussed in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a cross-sectional viewtaken along the center longitudinal axis of a torch incorporating theinventive principles disclosed herein,

FIG. 2 is a plan view of the structure shown in FIG. 1 looking in thedirection indicated by arrows 22, with portions of structure omitted.for the sake of clarlty, Y

FIG. 3 is a modification of the torch shown in FIGS. 1 and 2 and shownin cross-sectional view,

FIG. 4 is a general perspective view of the structure shown in FIG. 3,

FIG. 5 shows a modification of the electrode mounting arrangements ofFIGS. 1 and 3, but adapted for reach-in welding at a location away fromthe direction of reach-in,

FIG. 6 is a schematic view of an elementary circuit usable with thetorches shown in FIGS. 1-4 and 12.

FIGS. 7, 8, and 9 are further general schematic showings of differentcircuits which may be used with the various torches shown in the otherfigures.

FIG. 10 shows a cross-sectional view through a partially welded jointusing the torches disclosed in FIGS. 1-5,

FIG. 11 shows a keyhole type welded joint being made by a modified formof the device shown in FIG.

FIG. 12 shows a cross-sectional view corresponding generally with FIG. 1of a modification adapting the novel structure for use with consumableelectrode wire as associated with MIG welding,

FIG. 13 shows a cross-sectional view through a welded joint accomplishedby the apparatus and method suggested in FIG. 12,

FIG. 14 shows the arcing characteristic between the electrode andworkpiece of FIG. 12 during actual weld- FIG. 15 shows the gas flowpattern produced by the apparatus shown in FIG. 12 in relation to thesame workpiece components,

FIG. 16 shows a joint generally corresponding with the view shown inFIG. 13, but with the workpiece components misaligned horizontally,

FIG. 17 shows the electrode and workpiece relationship correspondingwith FIG. 12, but in an overhead welding position,

FIG. 18 shows a fragmented view, partly in crosssection and inperspective, of two workpieces adapted to be welded together using theapparatus shown in FIG. 12.

FIG. 19 shows the arcing characteristics of the electrode and workpieceshown in FIGS. 12 and 18, respectively,

FIG. 20 shows the joint resulting from the welding apparatus and methodsuggested in FIGS. 12, 18, and 19,

FIG. 21 shows two workpiece components adapted to be joined by theapparatus shown in FIG. 12,

FIG. 22 shows the welded joint resulting from the apparatus andstructure suggested in FIGS. 12 and 21,

FIG. 23 shows the general relationship between the apparatus shown inFIG. 12 for in--place casting of metal on a workpiece,

FIG. 24 shows the cast metal formed on a workpiece using the apparatusand method suggested in FIGS. 12 and 23, respectively, 7

FIG. 25 shows variations of the cross-sectional shape of various weldseams produced by the apparatus shown in FIG. 12 using differentoperational parameters,

FIG. 26 shows a schematic view of apparatus adapted for centrifugalcasting of workpieces using the structure shown in FIG. 12,

FIG. 27 shows a general perspective view of another modificationinvolving use of the apparatus shown in FIG. 12 for casting instead ofwelding, and

FIG. 28 is a perspective view in broken lines showing the gas flowpattern resulting from the operation of the structure in FIG. 12 inrelation to the workpiece components shown in the same figure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I, torch 8may be seen to include nonconsumable electrode 10 which is operativelyrelated to workpiece components 12 and 14 for progressively joining thesame along a path of travel generally aligned over gap 10 between theworkpiece portions.

Electrode 10 is releasably secured within a bushing or collet assembly18 supported in a holder 20 of any suitable type having electricalconnection between electrode 10 and a source of welding power (notshown). The structures comprising elements 10, 18, and 20 are known inthe prior art and may take various different forms now widely used inthe welding field. Most such electrode mounts include suitable passagemeans for connection with a remote source of inert gas (not shown), andfor flowing such gas around the electrode, as shown in FIG. 1 bypassages 15 and 17 within holder 20.

A gas cup 22, which may also be of conventional design known to theprior art, is secured to holder 20 by appropriate means which may takethe form of helical screw threads on both items 20 and 22 as shown bythreads 24 in FIG. 1. Cup 22 is preferably of dielectric material suchas ceramic, and functions to saturate the weld area with a suitableinert gas such as helium. For this purpose, cup 22 has connection meansat inlet 26 for receiving a flow of inert gas from an external source(not shown) through line 28. Inlet 26 communicates with annular passage30 which in turn communicates with area 32 within cup 22 through aplurality of spaced-apart passages 34, whereby a flow of gas from inlet26 is substantially uniformly distributed circumferentially within area32 and is downwardly directed as seen in FIG. 1 due to the confininginfluence of skirt portion 36 on cup 22.

As may be further seen from FIG. 1, a substantially closed chamber 40 ofgenerally elongate shape surrounds a portion of electrode 10 and issupported within cup 22 by suitable means such as threaded connectionsuggested by threads 42. Chamber 40 is provided with an end closureportion 44 which functions as a nozzle and is secured to chamber 40 bysuitable means which may illustratively take the form of threads 46interengaged between chamber 40 and end closure element 44. Element 44thus has the form of a substantially cylindrical inert, and is providedwith a center hole 48 having a size slightly larger than the crosssectional size of electrode 10, thus resulting in a small gap betweenthe electrode and the surface of hole 48 when the mentioned parts areassembled in the operative relationship shown in FIG. 1. Insert 44 isfurther provided with one or more holes or passages 50 radially spacedapart from hole 48 and orientated with respect to electrode 10 in aparticular manner as described further below. Preferably, the statedpassages 50 are at least four in number and are circumferentiallysituated about hole 48 and spaced apart from each other in asubstantially uniform symmetrical pattern such as suggested in FIG. 2.It will be understood that, whereas eight passages 50 are shown in FIG.2, that any number of passages larger or smaller than those shown can bemade to serve the same purpose without departing from the inventiveprinciples disclosed herein, and that the size and number of suchpassages will vary according to the size of nozzle element 44. Moreover,instead of a circular pattern, holes 50 may be arranged in otherpatterns either symmetrical or nonsymmetrical as desired to alter thedirectional characteristics of the plasma stream.

From the structure described above and shown in FIG. 1, it may be seenthat chamber 40 within closure means 44, when assembled in operativerelationship with holder 20 and the remaining structure thus disclosedforms a substantially enclosed area 52 which is adapted to function as aplenum chamber for inert gas supplied thereto through lines or passagesand 17 discussed hereinabove. When completely filled and pressurized byforceable entry of inert gas through lines 15 and 17, chamber area 52provides no other exit for the gas contained therein than holes 48 and50, whereby a plurality of high velocity gas jets or streams are formedby the stated apertures. Thus, as indicated by dotted lines 54 and 55 inFIG. 1, the conical slant of passages 50 relative to the long axis ofelectrode 10 causes high velocity inert gas jet streams to convergetoward each other and to intersect their direction of flow at a point 56which is situated within the location of the electrical are normallyproduced by flow of current from electrode 10 to workpiece portions 12and 14 when items 10, 12, and 14 are properly connected in a weldingcircuit.

As a result of the foregoing structural arrangement, the torch shown inFIG. 1 causes a significant portion of the high velocity gas exitingthrough passages 50 to be ionized upon penetrating the mentioned arc,whereby a plasma stream is produced substantially at the location ofpoint 56 and to flow downwardly through gap 16. The velocity of thestated gas from passages 55 must be sufficient to penetrate, andpreferably to pass through the stated arc, which normally exhibits avery high polarity. Inert gas supplied through line 28 and exiting fromarea 32 within cup 22 functions merely as a shroud to isolate the plasmastream from surrounding atmosphere. Thus, due to the extremely highvelocity of gas jets 54, 55 and energy activity in the plasma streamthus produced during operation of the device shown in FIG. 1, a verystrong jet pump or venturi action results in surrounding atmospherebecoming entrained in the gas and/or the plasma stream if an insulatingshroud of inert gas from area 32 is not provided. Such entrainment ofatmospheric gases would result in formation of metallic oxides andimpurities at the location of any contact area between the plasma streamand the workpiece material. Gas exiting through gap 48 surroundingelectrode 10 functions mainly to interfere with formation of a vortex atpoint 56 and does not appear to contribute significantly to the plasmaflow produced by the arc. Also, it has a very useful cooling effect onelectrode 10.

The modification shown in FIG. 3 includes means for preventingentrainment of surrounding atmosphere by the plasma stream created byelectorde 10 when the surrounding atmosphere is characterized by highpressure disturbances such as wind gusts which might occur during fielduse of the welding device. Thus, electrode 10 and mounting elements 18and 20 in FIG. 3 correspond with the same items shown in FIG. 1.However, cup 22 from FIG. 1 is replaced by two separate components whichare operatively related to perform the functions of cup 22 and chamberfrom FIG. 1 in a slightly different manner. Thus, a metallic disc-likehousing support 60 is secured to holder 20 by suitable means which mayillustratively comprise threads 62. Housing support 60 is in turnsecured to housing member 64 by appropriate means such as a plurality ofbolts 66 or the like which may be circumferentially spaced around thecenter axis of holder 20. Housing 64 may conveniently be of ceramic orother dielectric material to minimize the danger of accidental dischargebetween housing 64 and workpiece components 12 and 14. Housing 64 has aninner cavity 68 which functions as a plenum chamber in the same manneras area 52 within chamber 40 described hereinabove in connection withFIG. 1. Moreover, chamber 68 has an end closure member 70 in the form ofa substantially cylindrical and threaded insert having a plurality ofholes therein adapted to function in the same manner as insert 44discussed in connection with FIG. 1. Housing 64 is further provided withan annular cavity 72 which is substantially concentric with the longaxis of electrode 10 and which communicates with annular passage 74through a plurality of separate passages 76. Annular cavity 72 is thusadapted to receive a supply of inert gas through inlet line 78corresponding in function with line 28 described in connection with FIG.1, and to surround the arc normally created between electrode 10 andworkpiece components 12 and 14 with a curtain of the stated inert gas.Thus, gas within annular cavity 72 exists from the same through annulargap 80, the width of which may be varied by selection of differentdiameters of rings 82 and 84. Thus, annular cavity 72 is provided withhelical threads 86 and 88 on its inner and outer concentric walls, thestated threads oppositely corresponding with internal threads on ring 84and external threads on ring 82, respectively. The two stated rings areoperatively related when assembled in the relationship shown by FIG. 3whereby surface 90 on outer ring 82 is in confronting and spaced-apartrelationship with surface 92 on inner ring 84, the surfaces 90 and 92forming the outer and inner walls of gap 80, respectively. By varyingthe radial distance of surfaces 90 and 92 with respect to the long axisthrough electrode 10 using rings of different sizes in this respect, itwill be understood that the width of shape of gap may be adjustablyvaried to produce the mentioned shroud or curtain of gas flow. Theconfiguration thus shown by FIG. 3 is particularly adapted for field usewherein wind gusts or other atmospheric disturbances which coulddisplace or otherwise disrupt the protecting flow of gas from area 32 ofcup 22 in FIG. 1 is effec tively resisted by the higher velocity streamof inert gas which results from gap 80 in the torch of FIG. 3, andfurther suggested by FIG. 4.

A further modification of the device shown in FIG. 1 and particularlyadapted for reach-in welding at relaltively crowded or inaccessibleworkpiece areas may be seen in FIG. 5. Thus, reference numerals 94, 96,and 98 in FIG. 5 denote workpiece components structurally interrelatedwhereby welding is required to be done within a severely limited spaceenvelope and in a difection degrees from the direction in which awelding torch can be inserted from above in the view shown.

Electrode holder 20 and collet assembly 18, together with certain otherrelated components, may be seen to correspond with the same structureshown in FIG. 1. However, cup 22 in FIG. 1 is replaced in FIG. 5 by cup100 having a substantially 90 degree curvature between its upper end 102and exit skirt portion 104. Also,

chamber 40 seen in FIG. 1 is replaced in FIG. 5 by curved chamber 106having substantially the same shape and curvature as cup 100. Insert 108in FIG. 6 corresponds in shape and function with inserts 44 and 70 inFIGS. 1 and 3, respectively.

FIGS. 6 through 9 schematically suggest various types of circuits whichmay be used with the torches shown in FIGS. 1 through 5. Thus, FIG. 6shows a conventional type of welding circuit widely used and known inthe prior art. workpiece portion 12 or 14 is grounded or otherwiseconnected in circuit with power source 110 and torch 21 to create an arcas required for plasma generation.

FIG. 7 shows a circuit corresponding essentially with that taught in US.Pat. No. 3,319,043 issued May 9, 1967, wherein an arc is establishedbetween two electrodes in torches 21 and 23 which correspond either tothe structures shown in FIG. 1 or FIG. 3.

FIG. 8 shows a circuit essentially like that shown in FIG. 7 except thathollow elongate electrode 112 in FIG. 8 remains stationary whereas lowertorch 23 in FIG. 7 moves in unison with torch 21 in order to main tainsubstantial alignment between the two. Electrode 112 is cooled byappropriate means such as pump and water circulatory system 114, and isconnected in series with power source 110 and movable torch 21 wherebyan arc results between items 21 and 112 while workpiece components 12and 14 are not in circuit or grounded. Suitable heat and electricallyinsulated support means is provided for stationary electrode 112 asindicated at 116 in FIG. 8.

The circuit shown in FIG. 9 is generally similar to that shown in FIG.7, except that torches 21 and 23 are situated on the same side ofworkpiece components 12 and 14. An arc is struck between the two torchesas required to generate the plasma but the direction of plasma flow ispredominantly as indicated by dotted lines 118 and 120. In thearrangement shown by FIG. 9, the use of torches 21 and 23 for plasmawelding does not require a gap between the workpiece components asdiscussed hereinabove in connection with gap 16 shown in FIG. 1.

From the details set forth above, it may be seen that the inventiveconcept in this case may be used to convert welding electrodes currentlywell-known and widely used into plasma torches. The basic principle ofoperation involves a drastic increase in the amount of applied currentand the amount of inert gas above the amounts used during operation ofthe same device for welding. More importantly, the generation of plasmain the manner discussed hereinabove requires one or more powerful jetsof inert gas oriented so as to cause the stated jet or jets to penetrateor otherwise intersect the welding arc rather than flowing parallel tothe direction of welding current between electrode and the workpiece.Thus, the direction of ionizing gas flow is angularly disposed relativeto the direction of current flow at the location of the ionizing arc inall of the embodiments disclosed above.

closed herein. As a result, electrode erosion is not noticeably greaterwhen torch 8, for example, shown in FIG. 1 is used as a plasma generatorthan when used for conventional TIG welding. The foregoing feature isparticularly surprising when it is considered that much greater currentmay be applied when torch 8 is used to create plasma than when used forTIG welding. Thus, when electrode 10 in FIG. 1 is 0.090 inches diameter,the maximum current which could be safely applied to torch 8 when usedfor TIG welding has been found by actual test to be on the order of 200amps, beyond which the electrode, which is normally nonconsummable,would visibly disappear by reason of extremely rapid erosion. However,when electrodes of the stated diameter are used in torch 8 in the mannerdescribed above for plasma generation, a maximum current on the order of400 amps may be safely applied without any noticeable erosion effects onelectrode 10 resulting from such increase.

It is of further particular significance in this case that the torchesshown in FIGS. 1, 3 and 5 and discussed above are freely convertiblefrom plasma welding to conventional TIG welding without interrupting theflow of current to electrode 10. This performance feature is of specialusefulness in welding heavy-walled tubes or conduits such as in formingbutt-welded joints between adjacent conduit ends. In such joints, acomplete traverse of the electrode around the circumference of theconduit joint is made, and a small overlay weld is accomplished toinsure completion of the joint. During the initial traverse of theelectrode around two confronting conduit ends having a gap therebetweencorresponding to gap 16 shown in FIG. 1, it will be understood that thegap permits passage of the plasma stream from torch 8 through the gapand in close proximity to the confronting surfaces forming the same.However, when a plasma stream from torch 8 is applied to a surface toothick for the plasma stream to burn completely through, and in theabsence of a gap such as gap 16, the stream is impacted against thesurface and laterally displaced in all directions whereby control of theenergy thus applied for welding purposes is critically impaired.Accordingly, use of torch 8 of FIGS. 1 or 3 in the plasma generatingmode permits deep welding to be done during the initial traverse of thetorch around the heavy-walled conduit ends, as a result of which a weldbead is formed which closes the stated gap, after which any furtherwelding passes by torch 8 will normally require operation of the torchin the conventional TIG welding mode. Thus, referring to FIG. 10, weldbead 13 is formed during the initial pass of electrode 10 when operatingin the plasma generating mode to join workpiece portions 12 and 14.Additional welding passes as required to fill completely the gap betweenworkpiece portions 12 and 14 will require operation of electrode 10 inthe conventional TIG welding mode. Conversion from one mode to the otherusing torch 8, for example, shown in FIG. 1 involves merely a drasticreduction in flow rate of inert gas through apertures 48 and 50,accompanied by simultaneous reduction of current through electrode 10,such as from 400 amps to amps or less. The conversion step, since itinvolves only the operating parameters and no structural changes, may beaccomplished easily, automatically and rapidly.

Referring to FIG. 1, it is also a feature of torch 8 that the length ofelectrode 10 may be varied over a wide range such as to permit weldingwithin keyhole joints of the type shown in U.S. Pat. No. 3,099,740issued July 30, 1963. FIG. 2 of which is shown in modified form as FIG.11 of the drawings herein. In FIG. 11, torch 21 has an electrodecorresponding in all respects to electrode in torch 8 of FIG. 1 exceptthat it protrudes farther from the surrounding gas cup than electrode10, for reaching between face sheets 2 and 3 on a lightweight panelkeyhold type joint. The increase in length of electrode 10 protrudingfrom cup 22 of torch 21 in FIG. 11 is accompanied by a change in theangularity of holes 50 around the electrode such as required to directthe streams of gas from holes 50 to a new point 56 beyond the distal orunsupported end of the electrode.

It should further be noticed that all of the torches disclosed herein,both in the plasma and the conventional welding mode, are adaptable foruse with filler rod, consumable electrode or welding wire during thejoining process. It will further be understood that the type of jointwith which the torches disclosed herein may be used to accomplish a weldis not limited to butt joints or confronting spaced-apart surfaces suchas those which form gap 16 in FIG. 1, but may comprise surfaces in closeor coontinuous contact, lap joints, and others. Moreover, in the absenceof gap 16, it will be understood that plasma generated by torch 8 inFIG. 1 is capable of cutting through many different workpiece materialsprovided the same have sufficient thinness to result in burnthrough bythe plasma. Such burnthrough forms a small hole entirely through theworkpiece material which moves progressively along the welding path insubstantially continuous alignment with electrode 10, the base metal inthe workpiece closing together behind such burnhole. In the presence ofa gap such as gap 16, the molten material in workpiece components 12 and14 flows together to form a weld bead such as bead 13 shown in FIG. 10,as the torch moves past any given point along the welding path. In theabsence of the burnhole, such as when workpiece portions 12 and 14 arerelatively thick, the provision of gap 16 is necessary to permituniformity in the dominant direction of plasma flow generated by torch8.

The structure and method discussed herein provide a much greater rangeof variation in plasma flow velocity than is permitted by plasma torchesof conventional design known to the prior art. Thus, a relatively lowvelocity of inert gas through apertures 50 will result in acorrespondingly lowered velocity of the plasma stream resulting duringoperation of torch 8 in the plasma mode. This results partially from thefact that the arcing does not depend upon a particular volume of inertgas being applied thereto, and is not extinguished by sudden change ofinert gas velocity or rate through apertures 50. The are continues aslong as electrode 10 is positioned sufficiently close to workpiececomponents 12 of 14, or to another electrode as suggested in FIGS. 7 or8, while electrical power is supplied thereto. When excessive energy isapplied to the plasma srream, such as by increasing the flow of inertgas through apertures 50 in FIGS. 1 or 3, for example, the torches showntherein are very useful for metal cutting operations instead of welding,since molten metal is removed by the force of the plasma stream and thedwell time of the torch is increased above that associated with weldingoperation of the same torches. During welding operations, differences inarc length do not have such a critical effect on the amount of appliedenergy in the plasma stream as in conventional welding. Plasma flow willcontinue as long as the electrode is sufficiently close to the workpieceor to another electrode to maintain the are.

With particular regard to the inventive concept disclosed herein asapplied to MIG welding, a modification of the apparatus shown in FIG. 1may be seen in FIG. 12, wherein tungsten electrode 10 of FIG. 1 isreplaced by consumable electrode wire 11 in FIG. 12. Torch 8 in FIG. 12corresponds very closely with the structure shown in FIG. 1, as noted bythe similarity of reference numerals. However, holder 20 in thestructure shown by FIG. 12 does not include collet means 18 but has acenter hole therethrough adapted to make sliding contact with electrodewire 11 which is fed through holder 20 by suitable means (not shown) ina manner known to the prior art and including a reel 9. Notwithstandingthe close similarity between the welding torch configuration representedbetween FIGS. 1 and 12, a very different relationship may be seen toexist between electrodes 10 and 11 with regard to the workpiececomponents 12 and 14 in each of the stated figures. Thus, electrode 11is initially situated deeply within the weld zone whereby the distal tip101 of the electrode may protrude slightly below the lower surfaces 111and 113 of workpiece: elements 12 and 14, respectively. Gap 16 betweenthe stated workpiece components has sufficient width to admit thepassage of ionizing gas omitted from exit openings in the torch wherebyvirtually none of the stated gas flowing in the conical area defined bylines 54 and in FIG. 12 is diverted laterally before entering gap 16.The foregoing relationship between the torch and the workpiececomponents is particularly shown in FIGS. 14 and 15, the latterillustrating a substantially cylindrical plasma column 57-58, while FIG.14 shows that arcing occurs along the entire portion of electrode 11situated within gap 16 as suggested by lines 59. It has been found that,where gap 16 is of insufficient width to admit gas column 57-58initially, the gas forcibly penetrates the base metal and creates thenecessary space gap 16 to accommodate column 57-58. As a result of thearcing shown in FIG. 14, electrode 11 is rapidly consumed and must befed into the gap 16 from reel 9 at a relatively high rate duringprogressive fusion welding as torch 8 moves along the predetermined pathdefined by the gap. Moreover, it may be seen from FIG. 12 that workpieceelements 12 and 14 need no particular edge surface preparation prior towelding, and that confronting surfaces 124 and 126 of the workpieceportions 12 and 14 respectively, may terminate in substantially rightangle relationship with the upper and lower surfaces of each workpieceelement prior to welding. However, as a result of the arcingcharacteristic shown in FIG. 14, the stated angularity is alteredwhereby rounded corners 132, 134, 136, and 138 result due to erosion ofbase metal in the workpiece components during arcing. The weld seamresulting from the welding method thus shown in FIGS. 12, 14. and 15 maybe seen in cross-section in FIG. 13 and is designated by referencenumeral 128. Weld seam 128 has an enlarged width at each end thereof asshown by increased masses 127 and 129 in FIG. 13. During the foregoingwelding operation, particularly during downhand welding in the positionsuggested by FIG. 12, for example, it is desirable to use a backup orchill bar 131 of ceramic or other non-metallic material to arrest orimpede the flow of molten metal in weld seam 128. However, duringoverhead welding of workpieces l2 and 14 using the same apparatus andmethod suggested in FIG. 12, in the manner suggested by FIG. 17, forexample, no such backup bar or mess is required, since gravity forcenaturally prevents excess growth of the weld bead at its upper end,while rapid movement of the arcing area along gap 16 causes weld bead128 to cool before excessive drop-through occurs. Alternatively, a lowvelocity gas jet directed upwardly against the plasma column 57, 58 maybe used in place of ceramic mass 131 to perform the same function. Theforceful invasion of heat, gas and weld metal deeply within gap 16results in complete penetration of the joint in a single pass.

The welding process thus suggested in FIGS. l2, l4, and 15 isparticularly suitable in forming welded joints where the workpieceelements sought to be joined are not precisely formed or properlyaligned. Thus, FIG. 16 shows weld bead 130 between workpiece components12 and 14 which may be achieved even with such components misalignedhorizontally as suggested by distance x representing the measurementbetween lower surfaces 111 and 113 of components 12 and 14,respectively. lllustratively, welded joints such as suggested in FIG. 16have been successfully achieved with plates 12 and 14 having a thicknessof %inch each and displaced horizontally a distance x of 3/16 inch and agap 16 of l/] 6 inch, although the foregoing measurements do notrepresent limitations, and even greater misalignment could be possible.

The apparatus used in FIG. 12, for example, has been found to possessgreat versatility as a fabrication tool, useful in many differentwelding situations and processes in addition to other types of processesas discussed below. FIGS. 18 through 22 show two types of welded jointsuseful for securing together two plates or flange-like portions ofmetallic workpieces by one or more localized applications of weldingheat to form a welded rivet". In FIG. 18, workpiece element 150 ispreplaced in contact or at least in close proximity with workpieceelement 152 at the location where joinder therebetween is desired.Element 150 is provided with an aperture or opening 154 which may begenerally cylindrical in form, although the precise shape of opening 154is not critical. Moreover, opening 154 may be enlarged at one portionthereof, as suggested by generally conical surface 156 as distinguishedfrom cylindrical portion 158 in FIG. 18, for a purpose discussed below.With the workpiece elements arranged as shown in FIG. 18, welding isaccomplished by the apparatus shown in FIG. 12 by insertion of electrode11 within opening 154 as shown in FIG. 19. Arcing between electrode l1and workpiece components 150 and 152 simultaneous with gas flowsuggested by lines 54 and 55 in FIG. 19 results in penetration of thearc and the electrode into element 152 by creation of a cavity 160.Where element 150 is non-metallic or non-weldable, arcing is limited tothe space between electrode 11 and component 152, and will result incomplete filling of hole 154 with weld metal because arcing continues asthe weld puddle level rises within hole 154. The molten mass whichresults from melting of electrode 11 and base metal in elements 150and/or 152 solidifies upon cooling to form a rivet-like mass 164 as seenfrom the cross-sectional view of FIG. 20. Mass 164 has an enlargedportion at its outer end due to the conical portion 156 of opening 154initially formed in plate 150. Where no translational movement ofelectrode 11 occurs, mass 164 is of elongate and roughly cylindricalform such as a flathead nail and secures the workpiece elements togetherin fixed relationship in the general manner of a nail driven into twoplanks. Where hole 154 is an elongate gap to permit translationalmovement of electrode 11, mass 164 is a continuous weld seam instead ofa localized, roughly cylindrical mass.

FIG. 21 shows an alternative method for producing a weldment for thesame purpose as that shown in FIG. 20, but with separate holes 168 and169 formed in workpiece elements 150 and 152, respectively. It will beunderstood from FIG. 21 that holes 168 and 169 are roughly the same sizeand are formed in the workpiece elements before the welding operation isundertaken. Also, as suggested in FIG. 21, the holes need not be socarefully sized or located as to be in precisely coaxial matchingrelationship such as associated with rivet or bolt holes through twosheets or plates as practiced in the prior art. With plates and 152arranged as shown in FIG. 21, welding heat is applied to both elementsby insertion of electrode 11 in the apparatus shown by FIG. 12 in thesame general relationship as suggested between plates 12 and 14 in FIG.12. The resulting weld nugget 166 shown in FIG. 22, upon solidification,secures workpiece elements 150 and 152 to each other in fixedrelationship. The enlarged outer portions at each end of weldment 166shown in FIG. 22 is a natural occurrence and serves to strengthen theholding force of the weldment in the same manner as the two upset endsof a rivet, for example. The weldments discussed above in connectionwith FIGS. 18 through 22 are characterized by improved simplicity,rapidity, and economy over conventional mechanical holding means and areuseful in a wide variety of different applications, especially fluidtanks since they are self-sealing. Shrinking of the symmetrical nugget166 results in residual compressive force being continuously applied tohold the workpiece elements firmly together.

Referring to FIG. 23, the apparatus shown in FIG. 12 may be used forcasting molten metal in addition to its use for welding operations.lllustratively, containing means in the form of ceramic die blocks 170and 172 are preplaced on the surface of a workpiece such as' metallicplate 174. Workface surfaces 173 and 175 of blocks 170 and 172,respectively, are spaced apart a distance y to provide a gap withinwhich molten metal may be confined and formed. Operation of torch 8 withelectrode 11 positioned generally as shown in FIG. 23 results in adeposit of molten metal as the electrode is consumed by the are which isestablished between the electrode tip and workpiece 174. During torchoperation, the torch may be moved along a path of travel coincidinggenerally with the planview shape of the gap between blocks 170 and 172,whereby progressive casting in place of molten metal occurs. Aftercooling and consequent solidification of the metal thus deposited,blocks 170 and 172 are removed, leaving the cast structure as suggestedin FIG. 24 showing upstanding flange 176 integrally joined to workpiece174. The distal edge 178 of flange 176 may be ground flat as shown orotherwise shaped by subsequent machining operations where desired.

FIG. 25 shows four different weld nugget crosssectional shapes achievedby varying the operating parameters during use of torch 8 shown in FIG.12 to form weldments between workpiece elements 177 and 179. Weld seam180 may be seen to have substantially uniform width and results fromoptimum welding conditions wherein the welding wire feed rate ofelectrode 11 is properly balanced with regard to voltage level and flowrate of gas streams 54 and 55 during welding in the general mannersuggested by FIG. 12. Weld seam 182 shows the nugget cross-sectionalshape resulting from use of higher feed rate of electrode 11 than thatused for welding seam 180, but without a commensurate increase inwelding voltage. Weld seam 184 shows the characteristic cross-sectionalshape of the nugget resulting from decrease of wire feed rate ofelectrode 11 below that used during welding of seam 180 but without acommensurate lowering of welding voltage. Weld seam 186 is symmetricalabout a horizontal axis through the center thereof, but is wider at themidportion than at the two outermost ends thereof, and is achieved byincreasing the flow rate of the gas streams from nozzle exit openings 50in the torch shown by FIG. 12, without a commensurate increase ofvoltage or wire feed rate above those used in welding seam 180.

FIG. 26 shows a schematic view of apparatus such as may be used forcentrifugal casting and incorporating torch 8 as shown in FIG. 12. Theapparatus consists essentially of a rotor 190 having at least two radialarms 192 and 194 extending in opposite directions from rotor hub 190.Hub 190 and the elements secured thereto are adapted for rotation abouta center axis 188 by appropriate means such as bearings 196, 198, 200,and 202 supporting the stated hub. A hollow die block 204 is mounted onarm 192, while a counterbalance weight 206 is supported on arm 194 toequalize the forces applied to rotor 190 during rotation thereof. Dieblock 204 contains a cavity 208 having a shape corresponding to thedesired shape of the workpiece formed within the stated cavity. Torch 8is supported within arm 192 and suitably connected with a power source(not shown) for establishing an are between an electrode 11 and inlet211 of hollow die block 204. Plasma gas source 210 and rotatable reel212 are supported on rotor 190 as required to supply the operationalrequirements of torch 8 substantially in the manner suggested for theapparatus shown in FIG. 12. From the structure discussed above and shownin FIG. 26, it will be understood that operation of torch 8 producesmolten metal at inlet 211 due to the melting of electrode 11 which iscontinuously fed into the mentioned arc, and that simultaneous rotationof rotor 190 together with components secured thereto results incentrifugal force whereby the stated molten metal is forcibly directedinto cavity 208 to fill the same. Elaborate heating measures and theclogging of lines such as associated with centrifugal casting methodsknown to the prior art are avoided in the structure suggested by FIG.26, since molten metal is created precisely at the inlet of the diecavity adapted to receive the same, and only as much welding wire needbe consumed as is required to fill the die cavity, hence eliminatingwastage or overflow of casting metal of course, one skilled in the artwould provide a vent hole (not shown) that communicates with the mold sothat the gases, after they become neutralized, may be exhausted out ofthe vent hole. The same advantages may be seen to result from operationof the apparatus shown in FIG. 27.

FIG. 27 is a general perspective view of apparatus incorporating torch 8of the same structural configuration as shown in FIG. 12 for use incasting. The torch is secured on a rotatable arm 221 and connected bysuitable means to a source of ionizzable gas and a welding wire feedsystem. A multitude of individual casting dies 228 are arranged in acircle with inlet openings radially directed toward the exit of torch 8and closely proximate thereto. Hollow cavities within dies 228 arefilled individually and in progression by operation of torch 8 duringsimultaneous rotation of arm 221.

FIG. 28 shows a general perspective view of the gas flow patternresulting from operation of the torches shown in FIGS. 1 and 12, forexample, during downhand welding in the manner suggested particularly inthe latter figure. Passages 50 in torch 8 of FIGS. 1 and 12 define acircle about a vertical center axis 220 shown in FIG. 28, thediametrical axis being designated 224. Lines 54 and 55 of FIG. 28designate two diametrically opposite gas streams from two of passages 50in the torch nozzle surrounding electrode 11 which is concentric aboutaxis 220. All of the gas streams from passages 50 converge toward axis220 to form a circular pattern 226 having a diameter substantially equalto gap 16 between workpiece elements 12 and 14. Upon entering gap 16,the gas flow pattern remains substan tially uniform in width assuggested by cylindrical area portions 57 and 56 at each end of gap 16.The foregoing flow pattern results principally from the confininginfluence of workpiece elements 12 and 14 between which the gas orplasma stream flows during welding operations with torch 8. The amount,direction, and velocity of gas flowing from passages 50 are particularlysignificant in achieving the amazing results and advantages of theinventive concept disclosed herein. Thus, the total area 222 of theindividual gas streams exiting through passages 50 and forming theconical pattern between circles 223 and 226 must be substantially equalto the net cross-sectional area of the stream passing through gap 16.Any excess of such area in the conical portion of the flow pattern shownin FIG. 28 compared with the area of the cylindrical portion in suchpattern will result in lateral spillage of gas impacting the workpieceelements, such spilled gas being directed away from gap 16. Ideally,substantially all gas exiting from passages 50 should ultimately passthrough gap 16, it being understood that the cross-sectional area ofelectrode 11 is necessarily subtracted from the total area of circle 226to find the net flow area of the stream portions 57 and 58.

It will be understood that different gas flow rates, pressures,voltages, gas exit sizes, electrode sizes and other operating parametersmay be used in practicing the inventive concept disclosed and claimedherein, while still maintaining the precise relationship between gasflow characteristics discussed above. Accordingly, no particularoperating conditions should be regarded as critical in implementing theteachings contained herein. However, referring to FlG. 12, for example,carbon steel plates of ASTME grade 1035 having a thickness of inch and agap 16 of 0.025 inch have been welded without any edge preparation inthe manner suggested by FIG. 12 using about 38 volts and a gas flowthrough chamber 52 of about 50 cubic feet per hour of helium. Apertures50 in the foregoing instance had an area of 0.0016 square inch each andwere eight in number, for a total of 0.0128 square inch area. Electrodewire 1 1 had a diameter of 0.062 inch and center aperture 48 had adiameter of 0.081 inch. The included angle between diametricallyopposite holes 50 defined by the center lines thereof as suggested bylines 54 and 55 in FIGS. l2, l5, and 17, for example, was approximately18 degrees, although a variation from 16 to 20 degrees for the mentionedangle has been found to provide acceptable results. The wire feed rateof electrode 11 during the mentioned welding operation was 500 inchesper minute. The foregoing operating conditions produced a weld havingthe general form suggested by seam 180 shown, for example, in FIG. 25.

I claim: 1. A method for precision casting molten metal using a dieblock with an opening to receive molten metal, said method comprising:

positioning an elongated consumable metallic electrode adjacent saidopening, said electrode being made of said metal, forming an electricarc between said electrode and said die block so that said electrodemelts to produce said molten metal,

directing a stream of ionizable gas towards said arc and said openingwith sufficient force to penetrate said are and to cause said moltenmetal to form a stream and enter said opening so that said molten metalsolidifies within said die block, and

feeding said electrode into the arc to maintain the arc until said dieblock is filled with metal.

2. The method of claim 1 further includes the step of moving saidelectrode and said die block in a circle so that centrifugal forceaccelerates the molten metal into said die block to form a dense compactcasting.

3. The method of claim 1 further includes the steps of:

providing a plurality of die blocks arranged in a circle with theirrespective openings facing the center, and

moving said electrode in a circle as the arc is formed so that moltenmetal enters each die block in turn.

1. A method for precision casting molten metal using a die block with anopening to receive molten metal, said method comprising: positioning anelongated consumable metallic electrode adjacent said opening, saidelectrode being made of said metal, forming an electric arc between saidelectrode and said die block so that said electrode melts to producesaid molten metal, directing a stream of ionizable gas towards said arcand said opening with sufficient force to penetrate said arc and tocause said molten metal to form a stream and enter said opening so thatsaid molten metal solidifies within said die block, and feeding saidelectrode into the arc to maintain the arc until said die block isfilled with metal.
 2. The method of claim 1 further includes the step ofmoving said electrode and said die block in a circle so that centrifugalforce accelerates the molten metal into said die block to form a densecompact casting.
 3. The method of claim 1 further includes the steps of:providing a plurality of die blocks arranged in a circle with theirrespective openings facing the center, and moving said electrode in acircle as the arc is formed so that molten metal enters each die blockin turn.